Molded resin articles have been used as automobile components in recent years to reduce automobile weight. Resins such as ABS resins, PC/ABS resins, PPE resins, and polyamide resins have been used to achieve this object, and molded resin articles are often plated with copper, nickel, or the like to provide a high-quality impression and beautiful appearance. Further, a method for plating copper or the like on a resin substrate is used as a method for forming a conductor circuit by providing a resin substrate with conductivity.
A common method for plating a resin material such as a resin substrate or a molded resin article comprises degreasing and etching the molded article, optionally followed by neutralization and predipping, and then applying an electroless plating catalyst using a colloidal solution containing a tin compound and a palladium compound, optionally followed by activation (treatment with an accelerator), to perform electroless plating and electroplating sequentially.
In this case, a chromic acid mixture containing a mixed solution of chromium trioxide and sulfuric acid has been widely used as an etching treatment agent. However, chromic acid mixtures, which contain toxic hexavalent chromium, adversely affect work environments. Moreover, safe disposal of the liquid waste requires reduction of the hexavalent chromium to a trivalent chromium ion, followed by neutralization and precipitation, thus requiring complicated treatment for the disposal of the liquid waste. Therefore, in consideration of workplace safety and adverse effects of the liquid waste on the environment, avoiding the use of chromic acid-containing etching solutions is preferable.
Etching solutions containing a permanganate salt as an active ingredient are known as etching solutions that can be used in place of chromic acid mixtures. For example, Patent Literature 1 listed below discloses an acid etching solution containing a permanganate salt. Patent Literature 1 also teaches that various inorganic and organic acids can be used for adjusting the pH of the etching solution, and that sulfuric acid was used to adjust the pH to 1 or less in the Examples. Patent Literature 2 discloses an etching treatment agent containing a permanganate salt and an inorganic acid. However, such simple acid etching solutions containing a permanganate salt and an inorganic acid have poor bath stability, and the permanganate salt easily decomposes to generate sediment, thereby greatly reducing etching performance in short-term use.
Patent Literature 3 discloses an etching solution containing a permanganate salt and a periodic acid or a salt thereof, and having a pH of 2 or less, and that this etching solution improves bath stability. However, in the etching treatment of a resin material using the etching solution, an iodic acid, which is a by-product, reduces a permanganate ion, which is an active ingredient, thereby changing the bath composition, thus sometimes reducing etching performance.
Patent Literature 4 discloses a plastic surface modifier containing permanganic acid, phosphoric acid, and nitric acid, and optionally perchloric acid. Patent Literature 4 teaches that the use of the surface modifier increases the adsorption amount of a catalyst to a substrate in the catalyst application step, and improves deposit of plating; however, it nowhere discloses a method for inhibiting decomposition of permanganic acid.
As described above, various compositions are known as etching solutions without containing hexavalent chromium; however, the etching performance of the etching solution containing a permanganate salt is easily reduced by composition change over time, and further improvement in bath stability is desired.